1. Field of the Invention
Embodiments relate to methods to handle errors when transferring a chronological sequence of digital images.
2. Background of the Related Art
When transferring chronological sequences of digital images via a transmission channel, i.e., when transferring video data via telephone lines, data communication lines, or via a radio link, e.g., for video telephony, image data is transferred in digital form from one sender to one or more receivers. Frequently, as with video telephony, for example, audio data is also transferred together with the image data. The audio data thus frequently consists primarily of voice data, i.e., of digital representations of a voice signal produced by a person shown in the transferred images.
Due to the shift in technology from the traditional telephony to internet telephony (also known as Voice over IP or VoIP), value-added services that require more bandwidth between the communication participants are rapidly gaining significance. These can include real-time services (e.g., an audio transmission with high-quality codecs or video telephony), or parallel communication mechanisms without real-time requirements, as with so-called “messaging” or “chat.” Problems can arise with these value-added services, because they require that more bandwidth be available between the communication partners throughout the entire communication period. However, this requirement cannot always be supported, particularly with mobile communication partners that are reliant on wireless data communication. It is thus possible during a train ride where there was initially enough bandwidth for audio and video communication, for the quality of the network connection to subsequently dwindle such that the bandwidth required to conduct audio and video communication is temporarily unavailable.
To account for the limitations characterized by the properties of the transmission channel used with regard to the available bandwidth and any errors occurring, the image data and voice data to be transferred will be regularly “encoded.” The so-called encoding regularly reduces the data volume to be transferred with an irrelevance reduction and a redundancy reduction. To be able to protect the reference data (extensively) freed of redundancy from errors during the transfer, a certain amount of redundancy is regularly added again in the form of so-called error-correction codes.
For audio transmission, it is possible to react to a reduction in available bandwidth by dynamically switching to highly compressing codecs. In the area of video transmission, however, this is only possible to a very limited extent due to the substantial minimum bandwidth required for suitable moving image transmissions. If the available bandwidth falls below a certain value, today the image transmission will usually be adjusted, and depending on the implementation in the communication terminal, either no image will be shown at all, or a locally available contact photo will be shown, if applicable. This method is particularly unsatisfactory in the case of video conferences, because participants with insufficient bandwidth will have to participate in the conference in these cases without transferring their image, which causes them to be perceived as inadequate and makes them a second-class conference participant.